The present invention relates to a jettisonable element and a high speed missile utilizing same. More particularly, the present invention relates to a high speed missile including at least one jettisonable element that functions as a detachable cover protecting an optical window or dome from the external atmosphere, as a drag reduction element, and/or as a radar ghost when jettisoned.
The navigation of a missile to target is achieved using a guidance system. One or more guidance systems are generally employed. Radar is one such guidance system. Although radar is effective, it is subject to interference, both intentional interference deployed as a defense mechanism, and accidental interference resulting from environmental conditions. Therefore, radar is often employed in conjunction with optical or electro-optical guidance systems, either of which may operate in the visible or infrared portion of the spectrum. These guidance systems are composed of a sensor or a detection system (e.g., electro-optical camera), and an analyzing system. The detection system must be onboard, although the analyzing system may be located outside the missile, for example at a base on the ground or in a platform such as an airplane which launched the missile, which communicates with the missile during flight. Alternatively, both the detection system and the analyzing system are carried on-board. This alternative, referred to as a xe2x80x9claunch and forgetxe2x80x9d guidance system, is especially desirable in the case of missiles flying at high supersonic speeds where the time available for navigation decisions is extremely short, making communication with a remote location a practical impossibility.
The detection system must have a sensor in communication with the environment. At the same time, the sensor must be protected from the environment. For optical or electro-optical guidance systems this protection typically takes the form of an optical window or dome. These windows or domes are transparent to transmissions in a chosen range of wavelengths, while being opaque to transmissions with a wavelength outside that range. These optical windows or domes are typically coated with a shielding material which gives the window or dome the desired optical properties. As explained by D. Harris in xe2x80x9cMaterials for Infrared Windows and Domesxe2x80x9d (SPIE Optical Engineering Press, 1948), which is incorporated herein by reference, most common approaches to shielding include coating the optical window with an electrically conductive layer, covering the window with a metallic mesh, or increasing the conductivity of the material forming the window. In general, the thin electrically conductive coatings applied to the window are transparent at visible and/or infrared frequencies, but opaque to microwaves and radio waves. This makes such coatings useful in shielding sensitive electro-optical detectors against harmful electromagnetic interference (Kohin et al., SPIE Crit. Rev. CR 39:3-34(1992)). The shielding capabilities of these materials stems from their ability to reflect and/or absorb incident radiation. In general, the greater the conductivity of the coating material, the more effective the shielding. Common coating materials are described in, for example, (i) Pellicori and Colton (Thin Solid Films 209:109-115(1992)); (ii) Rudisill et al. (Appl. Opt. 13:2075-2080 (1974)), and (iii) Bui and Hassan (Proc. SPIE 3060:2-10(1997)), all of which are incorporated herein by reference. Since the conductivity of these materials decreases with increasing temperature, they lose their shielding effectiveness when they are heated. At the same time, transmission of desired wavelengths through the shield is often diminished by heating.
The use of missiles that include electro-optical detection systems is often constrained to near-sonic speeds, because at very high speeds (e.g., above several Mach), friction from the air causes heating of the optical window or dome which protects the electro-optical detection system. This heating changes the conductivity of the coating on the optical window or dome and as such alters the optical properties thereof. This results in incapacitation of the detection system of the missile, either because transmissions in the chosen range of wavelengths no longer pass through the window or dome, or because interference (transmissions with a wavelength outside the chosen range) is allowed to pass through the window or dome.
Consequently, prior art missiles flying at high speeds are substantially limited to radar guidance systems.
There is thus a widely recognized need for, and it would be highly advantageous to have, a cover for protecting an optical window or dome of missiles (and airborne platforms in general) from an external environment, which cover can be jettisoned to allow target acquisition by the optical payload when necessary. It would be of further advantage if the cover would also serve to reduce drag. Such a cover can also serve as a radar reflecting element, and as such produce a radar ghost when jettisoned.
According to the teachings of the present invention there is provided an airborne platform comprising: (a) an aerodynamic body; (b) a protected element within the aerodynamic body; and (c) a cover, reversibly secured to the aerodynamic body, for protecting the protected element from an external atmosphere.
According to another aspect of the present invention there is provided an airborne platform comprising: (a) an aerodynamic body; (b) an electro-optical detection system situated within the aerodynamic body, the electro-optical detection system being equipped with an optical window; and (c) a cover, reversibly secured to the aerodynamic body, for protecting the optical window from an external atmosphere.
According to further features in the described preferred embodiments, the airborne platform further includes: (d) a mechanism for at least partially detaching the cover from the aerodynamic body.
According to still further features in the described preferred embodiments, the airborne platform further includes: (e) a securing assembly for securing the cover to the aerodynamic body.
According to still further features in the described preferred embodiments, the cover is breakable, such that the releasing mechanism breaks the releasable element, thereby releasing the cover.
According to still further features in the described preferred embodiments, the releasing mechanism is operative to first act against the releasable element to unsecure the second end of the cover, and only subsequently to act against aerodynamic force, thereby detaching the second end of the cover from the aerodynamic body.
According to still further features in the described preferred embodiments, the securing assembly includes a hinge reversibly connecting a first end of the cover to a first region of the aerodynamic body, and a releasable element securing a second end of the cover to a second region of the aerodynamic body.
According to still further features in the described preferred embodiments, the hinge is configured such that when the second end of the cover separates from the second region of the aerodynamic body when the airborne platform is in flight, an aerodynamic force exerted by the external atmosphere on the cover detaches the hinge, thereby removing the cover from the aerodynamic body.
According to still further features in the described preferred embodiments, the hinge includes a stoppage element, the stoppage element serving for limiting an angular movement of the hinge such that when the second end of the cover separates from the second region according to a predetermined parameter, the force exerted on the cover breaks the cover in a predetermined location.
As used herein and in the claims section that follows, the term xe2x80x9cpredetermined parameterxe2x80x9d refers to a particular angle of rotation or a particular distance at which the cover and hinge structure is designed and made operative to detach the cover. In many hinges, the requisite separation of the cover from the second region for triggering the detachment of the cover can be defined either as an angle or as a distance (or some combination thereof).
According to still further features in the described preferred embodiments, the hinge includes an asymmetric ball element disposed in a socket. Thus, when the second end of the cover separates from the second region by a predetermined angle, the asymmetric ball element is rotated until disengagement from the socket, effecting spontaneous disassembly of the ball element.
According to still further features in the described preferred embodiments, this force includes an aerodynamic force exerted on the cover by the external atmosphere. According to still further features in the described preferred embodiments, this force includes a force delivered to the cover by the releasing mechanism.
According to still further features in the described preferred embodiments, the hinge includes a shearable pin.
According to still further features in the described preferred embodiments, the cover is operative to jettison away from the platform when released.
According to still further features in the described preferred embodiments, the cover includes at least one radar reflective region, such that the jettisoning of the cover from the airborne platform generates a radar ghost.
According to another aspect of the present invention there is provided a device for protecting an element in an airborne platform from an external atmosphere, the device comprising: (a) a cover, reversibly secured to an aerodynamic body of the airborne platform, for protecting the protected element from an external atmosphere; and (b) a mechanism for at least partially detaching the cover from the aerodynamic body.
According to further features in the described preferred embodiments, the cover is operative to jettison away from the platform when released.
According to still further features in the described preferred embodiments, the cover includes at least one radar reflective region, such that the jettisoning of the cover from the airborne platform generates a radar ghost.
According to still further features in the described preferred embodiments, the securing assembly includes a hinge for connecting a first end of the cover to a first region of the aerodynamic body, and a releasable element securing a second end of the cover to a second region of the aerodynamic body.
According to still further features in the described preferred embodiments, the device further includes: (e) a securing assembly for securing the cover to the aerodynamic body.
According to still further features in the described preferred embodiments, the releasing mechanism includes a high pressure gas reservoir as a source of energy for a force acting upon the releasable element.
According to still further features in the described preferred embodiments, the releasing mechanism includes a pyroelectric element as a source of energy for a a force acting upon the releasable element.
According to still further features in the described preferred embodiments, the releasing mechanism is designed to first act against the releasable element to unsecure the second end of the cover, and only subsequently to act against the aerodynamic force, thereby detaching the second end of the cover from the aerodynamic body.
According to another aspect of the present invention there is provided a method of protecting an element in an airborne platform, the airborne platform having an aerodynamic body, from an external atmosphere, the method comprising: (a) covering the element with a cover to the aerodynamic body; (b) securing the cover to the aerodynamic body; and (c) releasing and at least partially detaching the cover to expose the element.
According to further features in the described preferred embodiments, the securing of the cover is achieved using a hinge for connecting a first end of the cover to a first region of the aerodynamic body, and a releasable element for securing a second end of the cover to a second region of the aerodynamic body.
According to still further features in the described preferred embodiments, the releasable element is broken, thereby releasing the cover.
According to still further features in the described preferred embodiments, the releasing of the cover and the at least partially detaching the cover are performed by a releasing mechanism in discrete, sequential stages.
According to still further features in the described preferred embodiments, the releasing of the cover is performed in a first stage and the at least partially detaching of the cover is performed subsequently in a second stage, such that the releasing mechanism acts against aerodynamic force only in the second stage.
The present invention successfully addresses the shortcomings of the existing technologies by providing a system for and method of protecting airborne elements such as optical domes and windows from the air friction and the high temperatures generated while flying at high speed.